U.S. patent number 5,760,412 [Application Number 08/601,613] was granted by the patent office on 1998-06-02 for method and apparatus for sensing the presence of a line of data from a document on a transparent surface.
This patent grant is currently assigned to Microtek International, Inc.. Invention is credited to Wenhung Hsieh, Derek Tang, Chin-Sheng Yang.
United States Patent |
5,760,412 |
Yang , et al. |
June 2, 1998 |
Method and apparatus for sensing the presence of a line of data
from a document on a transparent surface
Abstract
Apparatus and a method for sensing the presence of a document on
the transparent surface of an optical scanner involve moving a
scanner optics carriage to a predetermined position beneath the
transparent surface, reading a line of data, and if any of the data
is on the "white" side of the gray-scale relative to a threshold,
determining that a document is present in the scanner. Optionally,
before determining whether a document is present, the apparatus and
method may perform an initial threshold comparison to check for the
presence of a dark background to ensure that an old document has
been removed before the new document is read. The results of the
document presence determination are used to generate a signal which
is sent through a scanner interface to the host computer for use in
automatically initiating a complete scan of a new document.
Inventors: |
Yang; Chin-Sheng (Hsinchu,
TW), Hsieh; Wenhung (Hsinchu, TW), Tang;
Derek (Hsinchu, TW) |
Assignee: |
Microtek International, Inc.
(Hsinchu, TW)
|
Family
ID: |
24408141 |
Appl.
No.: |
08/601,613 |
Filed: |
February 14, 1996 |
Current U.S.
Class: |
250/559.4;
250/234; 358/488 |
Current CPC
Class: |
H04N
1/00681 (20130101); H04N 1/00689 (20130101); H04N
1/00737 (20130101); H04N 1/00769 (20130101); H04N
1/00782 (20130101) |
Current International
Class: |
H04N
1/00 (20060101); G01N 021/86 () |
Field of
Search: |
;250/559.4,559.39,559.44,234 ;358/488,486,464,455,497 ;382/319,317
;355/75 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Le; Que
Attorney, Agent or Firm: Bacon & Thomas
Claims
We claim:
1. In an optical scanner including a transparent surface on which a
document is placed for scanning, a carriage, carriage positioning
means for causing the carriage to be moved relative to the
document, and reading means for capturing an image of the document
by capturing light reflected from the document through the surface,
the improvement comprising:
means for causing the carriage positioning means, prior to
initiation of a full scan in which said image of the document is
captured, to position the carriage at a location at which a line of
data from the document can be read when the document is placed on
the surface;
comparison means for comparing, with a threshold, data read by said
reading means after said carriage has been positioned at said
location by said carriage positioning means and prior to initiation
of a full scan to determine whether the document is present on the
surface;
means for generating, based on a result of said threshold
determination, a signal indicative of the presence of the document
on the glass, and means for initiating a full scan of the document
if the signal indicates the presence of the document on the
surface.
2. Apparatus as claimed in claim 1, wherein said document is a
document which has been newly placed on said surface, wherein a
previous document has been placed on said surface before said new
document, and further comprising means for making an initial
determination as to whether said previous document is present on
said surface, and for causing said comparison means to determine
whether said document is present on the surface only after said
previous document has initially been determined to be absent from
the surface.
3. Apparatus as claimed in claim 2, further comprising a pivotal
cover having a gray-scale value distinguishable from a gray-scale
value of a document.
4. Apparatus as claimed in claim 3, wherein said means for making
an initial determination as to whether a document is not present on
said surface comprises means for comparing a line of data with a
second threshold, and determining that a document is not present if
all data in said line of data is less than said second
threshold.
5. Apparatus as claimed in claim 4, wherein the first threshold is
equal to said second threshold.
6. Apparatus as claimed in claim 5, wherein said data is eight-bit
gray-scale data, and said first and second thresholds have a value
of hexadecimal 40 h.
7. Apparatus as claimed in claim 1, further comprising a pivotal
cover having a gray-scale value distinguishable from a gray-scale
value of a document.
8. Apparatus as claimed in claim 7, wherein a portion of said
pivotal cover is black.
9. Apparatus as claimed in claim 1, further comprising an interface
for connecting the scanner to host computer, and further comprising
means for transferring said signal to said host computer upon
receiving a status inquiry from the host computer, in order to
automatically inform the host computer that a document is in
position and that scanning may therefore begin.
10. Apparatus as claimed in claim 9, wherein said interface is a
SCSI interface.
11. A method of sensing the presence of a document positioned for
optical scanning on a transparent surface of a scanner, comprising
the steps of:
moving an optical sensing device into a document reading position
before initiation of a full-scan of said document;
reading a line of data;
comparing a grayscale level of the line read by the optical sensor
with a threshold after said optical sensing device has been moved
into said document reading position; generating a signal indicative
of the presence of a document on the surface depending on a result
of said comparing step, and initiating said full-scan if a document
is determined to be present on said surface.
12. A method as claimed in claim 11, wherein the signal generating
step comprises the step of generating said signal if a result of
said comparison is that the gray scale level of the line read is
greater than said threshold.
13. A method as claimed in claim 11, wherein said document is a
document which has been newly placed on said surface, wherein a
previous document has been placed on said surface before said new
document, and further comprising the steps of making an initial
determination as to whether said previous document is present on
said surface, and causing the step of comparing the gray-scale
level of the line of data with a threshold to occur only after said
previous document has initially been determined to be absent from
the surface.
14. A method as claimed in claim 13, wherein the step of making an
initial determination as to whether a document is not present on
said surface comprises the step of comparing a line of data with a
second threshold, and determining that a document is not present if
all data in said line of data is less than said second
threshold.
15. A method as claimed in claim 14, wherein the first threshold is
equal to said second threshold.
16. A method as claimed in claim 15, wherein said data is eight-bit
gray-scale data, and said first and second thresholds have a value
of hexadecimal 40 h.
17. A method as claimed in claim 1, wherein the scanner is
connected to a host computer via an interface, and further
comprising the step of transferring said signal to said host
computer upon receiving a status inquiry from the host computer, in
order to automatically inform the host computer that a document is
in position and that scanning may therefore begin.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an automatic document sensing apparatus
for use in an optical scanner, and to a method of automatically
sensing a document positioned in an optical scanner. The invention
also relates to firmware control of a scanner, and to a scanner
control program, preferably embodied in firmware, which enables
document sensing without the addition of mechanical, electrical,
and/or optical sensors.
2. Discussion of Related Art
Automatic document sensing apparatus in the form of mechanical or
electro-optical sensors are well-known in the art of document
handling, and are used, for example, in optical scanners having
automatic feed mechanisms. However, while scanners provided with
automatic document feed mechanisms have been known to include
document sensing mechanisms for initiating the document feed and
scanning process, the sensors used in scanner automatic feed
mechanisms are in general not suitable for use in scanners of the
type requiring manual document positioning.
The present invention is especially suitable for use in the latter
type of scanner, in which documents are manually positioned, one
page at a time, on a glass surface prior to scanning, and the only
way to signal the presence of a document and initiate scanning is
to manually manipulate a key, lever, switch, button, or other
device 1' on the scanner housing 1. While manual initiation of the
scanning process is not difficult, any added step in preparing a
document for scanning can be inconvenient in cases where multiple
documents are to be scanned or the scanner is located at a remote
location from the host computer.
An example of a commercially available scanner which includes a
document sensing function is the PageWiz.RTM. scanner manufactured
by MicroTek. This scanner uses an infrared sensor to detect a
document and initiate a paper loading process. The initial
detection occurs because the weight of the paper pushes the sensor
block up to a position where the document is positioned between the
sensor and a transmitter. While the PageWiz system is a user
friendly system, the mechanical components, additional sensors, and
electronics are complicated and would not be suitable for an
arrangement in which the document is manually positioned directly
on the sensor glass rather than automatically fed because 1.) it
would be very difficult to place a discrete sensing mechanism on or
near the glass surface, and 2.) the addition of such a mechanism
would in any case greatly increase the cost and complexity of a
scanner type whose principal advantages include simplicity and low
cost.
FIGS. 1 and 2 show a typical optical scanner of the type with which
the present invention is concerned, including a housing 1 and a lid
2 pivotally mounted at one end of a top surface of the housing. Lid
2 is arranged to cover a glass surface 3 on which a document to be
scanned is placed face down, so that the document can be read by
sensor elements which convert an image of the document into
electronic form for transfer to a host computer for storage and/or
processing. The sensor is typically a charge coupled device (CCD) 4
positioned within the housing and arranged to be at the focal point
of optical scanning elements in the form of mirrors 5-7 and a lens
8 which direct light reflected from the document to the CCD.
While it is possible to capture an entire image using a fixed array
of sensors and optical elements, in the typical scanner, for
purposes of convenience, the optical elements and sensors are
arranged to read a single line of the image at a time, with the
optical elements and sensor being stepped relative to the document
as each line is read. As shown in greater detail in FIG. 3, for
example, the optical elements may be arranged on a movable carriage
9, illustrated as including a guide 9' arranged to move along guide
rails (not shown), with illumination being provided by a lamp 10
arranged to move with the carriage. The image is thus formed as
light from lamp 10 is reflected from portions of a document
positioned on the glass and directed by mirrors 5-7 through a lens
and/or filter 8 to the CCD 4.
To compensate for changes in the light source and/or the
sensitivity of the CCD, it is conventional to include a calibration
strip in the form of a white strip 3' placed around the edge of the
glass surface. When not scanning, the carriage is normally
positioned beneath the calibration strip, where it stays until a
full scan is initiated.
The problem with this type of scanner, as indicated above, is that
in order to begin document scanning after a document has been
placed on the scanner, the operator must operate a switch, lever,
or other device 1' to indicate that the document is in position
ready for scanning and/or to initiate scanning. In the absence of
such an action, the host computer has no way of determining whether
the scanner is in fact ready to scan, and thus if the operator
forgets to operate the scan initiation device, the scanning program
will not work.
It is of course possible to determine whether a document is present
by scanning the entire document into the host computer and then
analyzing the results of the scan, but a complete scan takes time
and results in a waste of computer resources. To the contrary, the
current trend is to attempt to place as many of the scanner control
functions in firmware built into the scanner, simplifying the
software control requirements and also the operator interface.
Therefore, while the ultimate goal of the invention is for the user
to be able to simply place a document on the glass and have the
scanner automatically scan the document without having to touch a
scan key, it is also important to achieve the automated scanning in
a manner which does not require additional sensors, and yet which
can be achieved using firmware built into the scanner.
Although the invention is particular suitable for use in a scanner
of the type illustrated in FIGS. 1-3, achieving automated document
sensing using firmware which can be built into the scanner, it
should nevertheless be appreciated that the invention does not need
to be limited to the specific components illustrated in FIGS. 1-3.
For example, automated document sensing without additional sensors
could just as well be applied to scanners having an automatic feed
mechanism, but in which the document is stationary during a scan,
allowing the scan process to be synchronized with the automatic
feed, and also permitting verification that the feed mechanism has
properly positioned the document, without the need for additional
mechanical or electromechanical sensing elements.
SUMMARY OF THE INVENTION
It is accordingly an objective of the invention to provide an
apparatus and method for automatically sensing the presence of a
document on a scanner, without operator intervention.
It is a further objective of the invention to provide an apparatus
and method for automatically sensing the presence of a document on
a scanner of the type in which the document is placed face down on
a glass surface and an image of the document is captured one line
at a time by optical elements positioned on a movable carriage
below the glass surface.
It is a still further objective of the invention to provide an
apparatus and method for automatically sensing the presence of a
document on a scanner without the need for separate mechanical or
electro-optical sensor components, using scanner optics already
built into the scanner and control circuitry in the form of
firmware built into the scanner.
It is yet another objective of the invention to provide an improved
scanner having a document sensing function which eliminates the
need for operator intervention following positioning of a document
for scanning, and yet which does not require additional sensors or
complex sensing electronics that would significantly add to the
cost of the scanner, or increase the complexity of the host
computer scanner control software and interface.
These objectives of the invention are achieved, in accordance with
the principles of a preferred embodiment of the invention, by
providing apparatus in the form of firmware, and a method embodied
by program steps carried out by the firmware, for causing a scanner
optics carriage to move to a predetermined position relative to a
potential document, read a line prior to the initiation of a full
scan, and compare the line of data thus read with the threshold to
determine whether a document is present.
More particularly, the invention involves moving the scanner optics
carriage to the predetermined position beneath a dark portion of
the scanner lid, reading a line of data, and if any of the data is
on the "white" side of the gray-scale relative to the threshold,
determining that a document is present in the scanner. During this
determination, the line of data read is first converted to digital
values by the firmware and compared with a predetermined high-low
value, e.g., 40 h. If the result of such comparison is lower than
the predetermined threshold value, no new document is considered to
be on the glass and the scanner keeps reading it every few
mini-seconds until it gets data higher than the threshold.
In an especially preferred embodiment of the invention, two data
readings and two threshold comparisons are made before a scan is
initiated. The first comparison is to determine whether a document
is not present, so as to ensure that the scanner is clear of old
documents when the process is initiated, after which the
above-mentioned test for the presence of a new document is carried
out. In this preliminary step, the line of data read is first
converted to digital values by the firmware and compared with a
predetermined high-low value, e.g., 40 h. If the result of such
comparison indicates that any of the data is higher than the
predetermined threshold value (which can again be 40 h), an old
document is considered to be on the glass and the scanner keeps
reading it every few fractions of a second until all data is lower
than the threshold.
By way of background, the value 40 h is the hexadecimal equivalent
of the value 64 in an 8-bit grayscale system ranging from dark (0)
to white (255 or FFh in hexadecimal code). Those skilled in the art
will appreciate, however, that the invention is not to be limited
to a particular grayscale system or threshold value. The level
chosen as the threshold can, depending on such factors as the types
of documents to be scanned and the color of the background, be
freely varied so long as the threshold is between the background
level and the level of at least a portion of the document.
The above-described steps depend in part on the color of the inside
of the upper cover of the scanner, which is set to black in the
preferred embodiment of the invention. If there is no document on
the glass, the inside of the upper cover will be seen through the
glass. Since the inside of the upper cover is black, the first data
from a reading will be less than the threshold. If no new document
is placed on the scanner, the second reading will also be lower
than the threshold, and a no new document signal will be generated.
If there is a document on the glass before beginning the sensing
process, or the previous document has not been removed from the
glass, the auto scan will not start and the process will stay in
the first loop due to the fact the data is always above the
threshold.
The final aspect of the invention is its relation to the overall
scan process. In general, the invention works with a host computer
connected to the scanner through an appropriate two-way data
interface, such as a SCSI interface, which also permits
transmission of control signals or bits. The output of the document
sensing firmware is preferably in the form of a control bit,
referred to as a flag, having a document present value and a no
document value. In the preferred embodiment of the invention, the
flag is initially clear, indicating the lack of a new document,
until both threshold comparisons are made. The host computer reads
this flag periodically during execution of the scanner control
program, and uses the result to determine when to initiate a data
transfer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an optical scanner suitable for use
with the document sensing apparatus and method of the preferred
embodiment of the invention.
FIG. 2 is a schematic diagram of the principal optical components
of the scanner illustrated in FIG. 1.
FIG. 3 is a perspective view showing details of the optical
components illustrated in FIG. 2 and a carriage therefor.
FIG. 4 is a flowchart of the document sensing method of a preferred
embodiment of the invention.
FIG. 5 is a flowchart of the overall scanning initiation process of
the preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiment of the invention is implemented on a
scanner of the type illustrated in FIGS. 1-3, although it should be
appreciated by those skilled in the art that the details of the
scanner housing, optics, and carriage, are not critical to
operation of the invention, and that the principles of the
invention may be applied to a variety of scanner
configurations.
The critical elements of the invention are a transparent surface on
which the document is positioned for scanning, represented by glass
surface 3 illustrated in FIGS. 1 and 2, scanner optics capable of
reading a lines of data, represented by but not limited to mirrors
5-7, lens and/or filter 8, and CCD 4, illustrated in FIGS. 2 and 3,
and means for positioning the scanner optics so as to read a line
of data, represented by carriage 9 illustrated in FIG. 2.
Preferably, the scanner to which the present invention is applied
will include a lid corresponding to lid 2, although it is possible
that the invention could be applied to a scanner without such a lid
so long as background sensed by the CCD, absent a document, can be
distinguished from a document by thresholding.
Preferably, the invention is implemented in the form of firmware,
i.e., program instructions and data loaded in a class of memory
that cannot be dynamically modified during processing. The memory
can be in the form of a read-only memory, an electrically
programmable memory (EPROM or EEPROM), custom circuitry, or other
means of storing control information, together with registers and
the like for storing and transferring data used by the firmware. In
general, details of the firmware in question will be easily
implemented by those skilled in the art once the basic principles
of operation described in detail below are understood, particularly
since it is conventional to include firmware in optical scanners
for the purpose of controlling the main scanning operation, and the
present invention can therefore use, with simple modifications,
existing firmware and circuitry for moving the scanner carriage and
causing the scanner optics to read a line of data. As indicated
above, it is a trend to place more and more scanner control
functions in the form of firmware, although automated document
sensing has not previously been recognized as one of the scanner
control functions that can be implemented in the form of
firmware.
A flowchart of the basic document sensing process to be implemented
in the form of firmware as indicated above is illustrated in FIG.
4. The document sensing method begins upon power up, or upon
receipt of a ready signal or other indication of readiness, as
indicated by the "Start" symbol in the flowchart (step 100). In
this embodiment of the invention, the document detection routine
makes use of a flag "NewDocument" to indicate whether a document
has been sensed, the status of this flag being checked by a host
during the scanning process. This flag is initially cleared (step
110) and stays cleared until a two step document sensing routine is
completed.
The carriage which moves the scanner optics into position beneath
the document is initially positioned beneath the white border of
the glass area. As a result, the sensor carriage (step 120) must be
moved outside the boundaries of the white border so that the
scanner optics are positioned under a portion of the glass where a
document would be placed and a portion of the document can be
sensed. It will of course be appreciated that the particular area
sensed can be varied, and that it may also be possible to try
different areas during a single sensing operation to accommodate
different scanning positions or shapes and sizes of document,
although most scanners have one area which will be covered whenever
a document is placed on the glass regardless of the size or shape
of the document.
Upon moving the carriage outside of the white border area, it is
important that a contrast be provided so that the scanner can
recognize that a document is not present, which is why the lower
side of the lid is preferably a black color, so that the same
result will be obtained whether the lid is opened or closed, and so
that the lid will contrast with the lighter color of the paper use
in documents to be sensed. During the document scanning process, if
all of the data is within the range of a black background, then it
means that no document present. The control routine can then wait
for a document to be placed on the glass, after which scanning is
initiated.
The first step after movement of the carriage into the
predetermined position is to begin reading lines of data (step 130)
and comparing the level, conventionally a grayscale value, of the
received data with a predetermined threshold somewhere between
white and black (step 140). The level chosen as the threshold
should be dark enough to accommodate a variety of different types
of documents, but light enough to distinguish the black background.
For example, a suitable level could be grayscale 64 (40 h in
hexadecimal code).
At this point in the control routine, if the grayscale level of the
line is greater than the threshold, it means that the sensor is not
picking out the black background provided by the cover, or at least
is not sensing the absence of a document, which means that an old
document must be present on the glass. Thus, if any of the data is
greater than the threshold, the control routine returns to step
130, i.e., it initiates another read process after waiting a
suitable period of time, and repeats the comparison until all of
the data read is less than the threshold, indicating that the
document has been removed. The period of time that the read is
repeated can be varied, but should of course be short enough that
an old document cannot be replaced by a new document before a
second comparison takes place, and thus the wait time should not be
greater than a few milliseconds.
Once the control routine has determined that the scanner is ready
to receive a new document, based on the result of the first
thresholding, then another line of data is read (step 150) and the
scanner seeks to determine whether a document is present on the
glass by comparing the data read with a second threshold (step
160).
In the illustrated embodiment, the second threshold is the same as
the first threshold, i.e., 40 h, although it is within the scope of
the invention to vary the second threshold. Rather than seeking to
determine whether all of the data is below the threshold, as in the
first comparison, however, the second comparison seeks to determine
whether any of the data is above the threshold. While this is
simply the negative of the original determination, and can be
implemented using exactly the same subroutine, the results of the
determination are that if none of the data is greater than the
threshold, the routine clears the "NewDocument" flag is it has
previous been set to indicate the presence of a new document (step
170) and returns to the beginning of the new document detection
portion of the routine, while if any of the data is greater than
the threshold, the "NewDocument" flag is set (step 180) and the
routine then checks for the absence of a document.
Those skilled in the art will appreciate that, in the case where
the first and second thresholds are the same, the routine can
return from step 180 to step 150 since, as soon as the document is
removed, the loop will switch from step 180 to step 170 and the
"NewDocument" flag will be cleared, which is the same effect as
returning to step 130.
Turning to FIG. 5, which illustrates the scanner as being connected
to the host computer via a SCSI interface, although those skilled
in the art will appreciate that other interfaces, such as a
parallel interface, could be used, the "NewDocument" flag may be
used by the scanner and host computer, as follows: On the host
side, after the operator begins the scanner program, polling is
initiated by the host program (step 200) and the host periodically
polls the scanner by issuing an inquiry to the scanner (step 210)
to obtain the scanner status. In the case where the scanner is
connected to the host computer by a SCSI interface 12, the inquiry
simply checks the appropriate pin on the interface for presence of
a voltage on the pin (step 220), the presence or absence of the
voltage indicating the status of the "NewDocument" flag. If the
"NewDocument" flag is set, the host issues a scan command (step
230) and then proceeds through the normal scanning routine (step
240). If the "NewDocument" flag is clear, or the scanning process
has been completed, the host control routine returns to the
beginning of the loop in order to begin polling for a new
document.
On the scanner side, as illustrated in FIG. 5, the presence of a
signal on an interrupt line of the SCSI interface may be used to
initiate the document scanning process, beginning with step 100, or
simply to cause the results of steps 170 and 180, i.e., the
contents of the "NewDocument" flag, which could simply be the
output of a comparator or register, to be forwarded to the
interface. For purposes of illustration, the scanner side steps are
labelled inquiry (step 300), update (step 310), and return (step
320). It will be appreciated by those skilled in the art that
additional steps may be required where the interface is, for
example, a parallel interface.
Having thus described various preferred embodiments of the
invention, those skilled in the art will appreciate that variations
and modifications of the preferred embodiment may be made without
departing from the scope of the invention. It is accordingly
intended that the invention not be limited by the above description
or accompanying drawings, but that it be defined solely in
accordance with the appended claims.
* * * * *